1. Field of the Invention
The present invention relates to banked purification systems, particularly systems having a bank of two or more purification columns in which fluid is purified by a purifying component.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Purification columns are commonly used to purify fluids (gases or liquids) by passing the fluid through the column, contaminants or other unwanted parts of the fluid being extracted from the fluid by a purifying component, such as an absorbent, adsorbent, filter etc., contained in the column. For example, purification columns can be used as: compressed air and gas dryers, gas generators (e.g. generation of N2 by removal of O2 and CO2 from air), dust filters, refrigerant filters, vacuum pump filters, oil mist filters, etc.
In banked purification systems, a plurality of purification columns is used to increase the fluid flow capacity, the number of banked columns in a given system depending on the flow rate requirement of the particular application.
Some purifying components can be re-generated in-situ. For example desiccants, such as activated alumina and molecular sieve materials used to remove moisture from compressed air and gas, may be re-generated using pressure swing technology, vacuum technology and/or heat regenerative technology. On the other hand, if the purifying component cannot be re-conditioned in-situ it may have to be replaced at regular intervals. For example, when activated carbon is used to remove hydrocarbon contamination from compressed air and gas, the carbon is generally replaced once spent.
It is common practice to use welded and fabricated carbon steel or stainless steel pressure vessels as purification columns. Typically, such vessels have internal diameters from 4 inches (10.2 cm) to over 72 inches (182.9 cm). Due to their manufacturing processes, they are relatively expensive. Furthermore such pressure vessels have to be manufactured in accordance with codes of practice for pressure equipment. Thus, in recent times, it has become popular to replace large single steel pressure vessels with multiples of smaller diameter extruded aluminium tubes, the tubes being banked for larger flow rates. Such extruded tubes are relatively inexpensive to manufacture.
It is common to use aluminium alloy tube columns with internal diameters of up to a maximum of 6 inches (150 mm), as such diameters tend to fall outside of the scope of some of the common pressure vessel design codes and rules.
The use of such columns results in a flexible, banked purification system in which the number of columns can be varied to reflect the flow rate of fluid which needs processing.
Conventional banked systems use separate top and bottom (inlet and outlet) manifolds between which the bank of columns is sealed and clamped. The process fluid is divided at the inlet manifold into separate streams which then flow through respective columns before recombining at the outlet manifold.
However, the inlet and outlet manifolds can be expensive to manufacture. Further, each manifold requires a fixed number of banked columns, making it inconvenient and expensive to change the flow capacity of the system by varying the number of columns. For example, typical manifolds can be for 2, 4, 6, 8, 10 or 12 banked columns, and if it is desired to vary the flow capacity of the system then some or all of these manifolds would have to be replaced, which is generally cost prohibitive. Furthermore from a manufacturing standpoint the manifolds would either have to be made to order, which extends delivery time or each manifold size would have to be held in stock, which increases stock value. Therefore existing multi-bank systems using top and bottom manifolds are not very flexible in a production environment, as extra components have to be held in stock which in turn increases manufacturing costs.
In addition, a further disadvantage of conventional banked systems can be the complex methods of bolting used to hold the columns in place. This can create substantial assembly costs and more importantly substantial maintenance costs when replacing a purifying component. For example, when a large number of fastening bolts are used, it may be necessary, upon re-assembly, to tighten the bolting in a particular sequence with torque wrenches in order to achieve a uniform clamping force and create pressure tight seals. The manifolds themselves may also be large and cumbersome to remove and/or replace.
Generally, associated pipework is directly connected to the manifolds and this will also have to be dismantled or disconnected during maintenance. With the inevitable re-assembly of the associated pipework, this has further adverse effects on maintenance times and costs.